1. Technical Field
This invention pertains to integrally molded composite articles. More particularly, this invention relates to integrally molded composite panels comprising a foamed plastic core and a polynorbornene outer layer. The polynorbornene outer layer is composed of at least one norbornene type monomer which is polymerized around the core material via ring-opening bulk polymerization.
2. State of the Art
Composite molded products consisting of a foam core and an outer layer of unsaturated polyester, epoxy resin, phenolic resin, polyurethane resin, and the like are lightweight and, therefore, are often used in the production of leisure goods such as sailboards, surf boards, boats, and ores.
These composite products are manufactured by manually winding reinforcing fibers such as glass fibers around a foam core and applying a thermosetting resin to the core-fiber composite, followed by curing (also known in the art as the hand lay-up method). This method is unsuitable for mass production because of the intensive manual labor involved.
In another method, a foam core is wrapped with glass, carbon, or aramid fibers, and placed in a mold. A liquid thermosetting polymer is conveyed to the mold and thermally cured to prepare a composite molded product as disclosed in Japanese Kokai application Ser. No. 63-16220. In this method, evenly wrapping the core with reinforcing fibers is difficult. In the case of glass fibers, broken fiber pieces tend to prick hands, face, and body, creating an uncomfortable work environment. Furthermore, when a reinforcing fiber wrapped foam core is placed in a mold and a thermosetting type monomer is polymerized thereabout, the resulting product has a weak outer layer because of the lack of reinforcement therein. For sufficient strength, a costly epoxy resin must be used.
When reinforcing fibers are used in the outer layer, the reinforcing material tends to be exposed at or slightly below the surface of the molded product, making it difficult to obtain a smooth surface.
When dicyclopentadiene is bulk polymerized in a mold in the presence of a metathesis catalyst, a molded product with high rigidity and high impact strength is obtained. In this way, a large molded product is readily manufactured. In an attempt to prepare an integrally molded composite with a foam core and an outer polynorbornene layer, the present inventors placed a precast foam block (that was sliced or cut to a desired shape and size) into a mold. A low viscosity reaction solution containing a norbornene type monomer was conveyed to the mold under low pressure and polymerized. Due to the low molding pressure, the foam core was not damaged or deformed in the molding process. An integrally molded (non-reinforced) composite with good strength was obtained. However, when large molded composite products are manufactured in this manner, the surface of the product often has voids, indentations and bumps. Moreover, when a foam core with a high foaming ratio is used, intimate bonding between the core material and outer layer is not achieved. Consequently, wavy defects appear in the product.
Accordingly, there is a need for a strong, lightweight integrally molded composite product without any surface defects.